This invention relates to photographic systems of the type employing multi-purpose film cassettes in which a strip of photographic film contained in such a cassette, is exposed, processed and projected by appropriate manipulation of the cassette without removal from the cassette. More particularly, it concerns a novel method and apparatus for processing the exposed film strip in the cassette under accurately controlled and uniform temperatures.
In U.S. Pat. No. 3,800,306 issued Mar. 26, 1974 to Edwin H. Land, there is disclosed a photographic system particularly suited to motion picture application in which a film cassette containing a strip of photographic film, a supply of processing fluid and a processor operative to apply the processing fluid to the film strip upon manipulation thereof in the cassette is first mounted in an appropriate camera for incremental exposure along the length of the film strip in accordance with conventional motion picture film strip exposure techniques. During the exposure cycle, the film strip is advanced from a supply spool on which it is initially wound in the cassette to a take-up spool about which all of the film is wound after exposure with the exception of a supply spool leader which extends back to and is permanently connected to the supply spool. Following exposure of the film strip, the cassette is removed from the camera and inserted in a film drive and projection system or viewer adapted to receive the cassette and which is responsive to the condition of the film in the cassette to effect either a processing cycle in which the strip is rewound during the application of the processing fluid to the emulsion side of the film strip or a projection cycle in the event the film contained in the cassette has been processed previously.
The processing cycle of operation in the system disclosed in the aforementioned patent is carried out by driving the supply spool in a direction of rewind rotation to effect first a removal of a tear tab closure from an initially sealed supply reservoir or pod of processing fluid. The viewing apparatus is programmed so that subsequent to the removal of the tear tab closure and release of processing fluid, rewind drive of the strip is interrupted for the duration of a short time delay to enable gravity flow of the processing fluid to an applicator nozzle overlying the emulsion side of the film strip and which forms part of the processor contained in the cassette. After the time delay, the supply spool rewind drive in the viewer is again actuated to advance the film strip at constant speed under the applicator nozzle so that a uniform layer of processing fluid is deposited on the film strip along the entire length thereof. The processing fluid reacts chemically with the exposed, light sensitive emulsion on the film strip to develop the latent negative image within the emulsion layer and transfer a positive image to a positive image receiving layer. The attainment of a defect-free series of positive images on the film strip in this manner is dependent on the uniformity of processing fluid deposition during the processing cycle. To this end, the processor disclosed in the aforementioned U.S. patent incorporates an inclined doctoring surface in the nozzle applicator against which the film strip is retained by a yieldable pressure pad bearing against the opposite side of the film strip. The hydrodynamic pressure gradient resulting from this organization assures a uniform doctoring or buttering of the processing fluid across the width of the film strip and along the entire length thereof. Upon completion of the processing cycle, a surface discontinuity in the take-up spool leader of the film strip or at the end of the film strip last to be processed engages a valve member provided in the cassette and moves it into closing relationship with the applicator nozzle opening. This assures containment of residual amounts of processing fluid which may be present in the processor and which could be deleterious to the processed film strip until such time as it evaporates. In addition to containing residual amounts of processing fluid, the valve member movement is from a condition in which a pair of electrical contacts are in circuit continuity to one of circuit discontinuity. Such contacts or terminals on the cassette are engaged by mating contacts in the viewing apparatus to enable the latter to sense the processed or unprocessed condition of the film strip in a given cassette.
Although the system disclosed in the aforementioned U.S. patent represents a highly sophisticated advance particularly in the motion picture art, proper processing of the exposed film is vital to basic system objectives inasmuch as any defect in the processing operation is likely to cause permanent blemishes in the positive image transparencies carried by the film strip and which are visible during subsequent and repeated projection cycles. It is important, therefore, that the conditions under which the processing operation is carried out be maintained as favorable as possible both from the standpoint of facilitating the action of the processing fluid on the exposed emulsion and from the standpoint of minimizing the duration of time the processing fluid is maintained in a liquid or semi-liquid state after deposition on the emulsion side of the film strip. In these latter respects, it is known in the prior art that diffusion transfer processing of photographic films is enhanced where such processing takes place at constant temperature and also that the rate of image development and transfer is increased at temperatures slightly above normal room temperatures. See, for example U.S. Pat. No. 2,576,022 issued Nov. 20, 1951 to E. H. Land; U.S. Pat. No. 2,794,377 issued June 4, 1957 to M. N. Fairbank; U.S. Pat. No. 3,143,950 issued Aug. 11, 1964 to E. W. Elliott et al.; and U.S. Pat. No. 3,608,456 issued Sept. 28, 1971 to A. H. Hauser.
With the exception of the patent to Elliott et al, each of these prior art references disclose self-developing still cameras in which discrete prints are formed using the diffusion transfer developing process and in which the processing fluid or liquid is spread between or supplied in a temporary covering sheet overlying the sheet on which the positive print is formed and ultimately viewed after removal of the covering sheet. In the Elliott et al patent, the continuous strip of photographic film is fed from a supply cassette through a camera to a separate takeup cassette in which the exposed film is wound concurrently on a spool with a web saturated with processing liquid. Visual observation of the prints developed on the film strip is possible only after the assembly is further manipulated by removal of the processing web from the developed film. While these references therefore recognize the desirable attributes of an elevated constant temperature environment for diffusion transfer processing of film, none of these references is concerned with film strip processing in which the processing fluid is deposited as a liquid directly onto the film strip to develop images capable of being immediately and directly viewed by projection.